minstrel-ht-wifi-manager.h

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/*
 * Copyright (c) 2009 Duy Nguyen
 * Copyright (c) 2015 Ghada Badawy
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 *Authors: Duy Nguyen <duy@soe.ucsc.edu>
 *         Ghada Badawy <gbadawy@gmail.com>
 *         Matias Richart <mrichart@fing.edu.uy>
 *
 * MinstrelHt is a rate adaptation algorithm for high-throughput (HT) 802.11
 */
 
#ifndef MINSTREL_HT_WIFI_MANAGER_H
#define MINSTREL_HT_WIFI_MANAGER_H
 
#include "minstrel-wifi-manager.h"
 
#include "ns3/wifi-remote-station-manager.h"
#include "ns3/wifi-types.h"
 
namespace ns3
{
 
/**
 * Data structure to save transmission time calculations per rate.
 */
typedef std::map<WifiMode, Time> TxTime;
 
/**
 * @enum McsGroupType
 * @brief Available MCS group types
 */
enum McsGroupType
{
    WIFI_MINSTREL_GROUP_INVALID = 0,
    WIFI_MINSTREL_GROUP_HT,
    WIFI_MINSTREL_GROUP_VHT,
    WIFI_MINSTREL_GROUP_HE,
    WIFI_MINSTREL_GROUP_EHT,
    WIFI_MINSTREL_GROUP_COUNT
};
 
/**
 * @brief Stream insertion operator.
 *
 * @param os the stream
 * @param type the MCS group type
 * @returns a reference to the stream
 */
inline std::ostream&
operator<<(std::ostream& os, McsGroupType type)
{
    switch (type)
    {
    case WIFI_MINSTREL_GROUP_HT:
        return (os << "HT");
    case WIFI_MINSTREL_GROUP_VHT:
        return (os << "VHT");
    case WIFI_MINSTREL_GROUP_HE:
        return (os << "HE");
    case WIFI_MINSTREL_GROUP_EHT:
        return (os << "EHT");
    default:
    case WIFI_MINSTREL_GROUP_INVALID:
        return (os << "INVALID");
    }
}
 
/**
 * Data structure to contain the information that defines a group.
 * It also contains the transmission times for all the MCS in the group.
 * A group is a collection of MCS defined by the number of spatial streams,
 * if it uses or not Short Guard Interval, and the channel width used.
 */
struct McsGroup
{
    uint8_t streams;   ///< number of spatial streams
    Time gi;           ///< guard interval duration
    MHz_u chWidth;     ///< channel width
    McsGroupType type; ///< identifies the group, \see McsGroupType
    bool isSupported;  ///< flag whether group is  supported
    // To accurately account for TX times, we separate the TX time of the first
    // MPDU in an A-MPDU from the rest of the MPDUs.
    TxTime ratesTxTimeTable;          ///< rates transmit time table
    TxTime ratesFirstMpduTxTimeTable; ///< rates MPDU transmit time table
};
 
/**
 * Data structure for a table of group definitions.
 * A vector of McsGroups.
 */
typedef std::vector<McsGroup> MinstrelMcsGroups;
 
struct MinstrelHtWifiRemoteStation;
 
/**
 * A struct to contain all statistics information related to a data rate.
 */
struct MinstrelHtRateInfo
{
    /**
     * Perfect transmission time calculation, or frame calculation.
     * Given a bit rate and a packet length n bytes.
     */
    Time perfectTxTime;
    bool supported;      //!< If the rate is supported.
    uint8_t mcsIndex;    //!< The index in the operationalMcsSet of the WifiRemoteStationManager.
    uint32_t retryCount; //!< Retry limit.
    uint32_t adjustedRetryCount; //!< Adjust the retry limit for this rate.
    uint32_t numRateAttempt;     //!< Number of transmission attempts so far.
    uint32_t numRateSuccess;     //!< Number of successful frames transmitted so far.
    double prob; //!< Current probability within last time interval. (# frame success )/(# total
                 //!< frames)
    bool retryUpdated; //!< If number of retries was updated already.
    /**
     * Exponential weighted moving average of probability.
     * EWMA calculation:
     * ewma_prob =[prob *(100 - ewma_level) + (ewma_prob_old * ewma_level)]/100
     */
    double ewmaProb;
    double ewmsdProb;            //!< Exponential weighted moving standard deviation of probability.
    uint32_t prevNumRateAttempt; //!< Number of transmission attempts with previous rate.
    uint32_t prevNumRateSuccess; //!< Number of successful frames transmitted with previous rate.
    uint32_t numSamplesSkipped;  //!< Number of times this rate statistics were not updated because
                                 //!< no attempts have been made.
    uint64_t successHist;        //!< Aggregate of all transmission successes.
    uint64_t attemptHist;        //!< Aggregate of all transmission attempts.
    double throughput;           //!< Throughput of this rate (in packets per second).
};
 
/**
 * Data structure for a Minstrel Rate table.
 * A vector of a struct MinstrelHtRateInfo.
 */
typedef std::vector<MinstrelHtRateInfo> MinstrelHtRate;
 
/**
 * A struct to contain information of a group.
 */
struct GroupInfo
{
    /**
     * MCS rates are divided into groups based on the number of streams and flags that they use.
     */
    uint8_t m_col;               //!< Sample table column.
    uint8_t m_index;             //!< Sample table index.
    bool m_supported;            //!< If the rates of this group are supported by the station.
    uint16_t m_maxTpRate;        //!< The max throughput rate of this group in bps.
    uint16_t m_maxTpRate2;       //!< The second max throughput rate of this group in bps.
    uint16_t m_maxProbRate;      //!< The highest success probability rate of this group in bps.
    MinstrelHtRate m_ratesTable; //!< Information about rates of this group.
};
 
/**
 * Data structure for a table of groups. Each group is of type GroupInfo.
 * A vector of a GroupInfo.
 */
typedef std::vector<GroupInfo> McsGroupData;
 
/**
 * @brief Implementation of Minstrel-HT Rate Control Algorithm
 * @ingroup wifi
 *
 * Minstrel-HT is a rate adaptation mechanism for the 802.11n/ac/ax standards
 * based on Minstrel, and is based on the approach of probing the channel
 * to dynamically learn about working rates that can be supported.
 * Minstrel-HT is designed for high-latency devices that implement a
 * Multiple Rate Retry (MRR) chain. This kind of device does
 * not give feedback for every frame retransmission, but only when a frame
 * was correctly transmitted (an Ack is received) or a frame transmission
 * completely fails (all retransmission attempts fail).
 * The MRR chain is used to advise the hardware about which rate to use
 * when retransmitting a frame.
 *
 * Minstrel-HT adapts the MCS, channel width, number of streams, and
 * short guard interval (enabled or disabled).  For keeping statistics,
 * it arranges MCS in groups, where each group is defined by the
 * tuple (streams, GI, channel width).  There is a vector of all groups
 * supported by the PHY layer of the transmitter; for each group, the
 * capabilities and the estimated duration of its rates are maintained.
 *
 * Each station maintains a table of groups statistics. For each group, a flag
 * indicates if the group is supported by the station. Different stations
 * communicating with an AP can have different capabilities.
 *
 * Stats are updated per A-MPDU when receiving AmpduTxStatus. If the number
 * of successful or failed MPDUs is greater than zero (a BlockAck was
 * received), the rates are also updated.
 * If the number of successful and failed MPDUs is zero (BlockAck timeout),
 * then the rate selected is based on the MRR chain.
 *
 * On each update interval, it sets the maxThrRate, the secondmaxThrRate
 * and the maxProbRate for the MRR chain. These rates are only used when
 * an entire A-MPDU fails and is retried.
 *
 * Differently from legacy minstrel, sampling is not done based on
 * "lookaround ratio", but assuring all rates are sampled at least once
 * each interval. However, it samples less often the low rates and high
 * probability of error rates.
 *
 * When this rate control is configured but non-legacy modes are not supported,
 * Minstrel-HT uses legacy Minstrel (minstrel-wifi-manager) for rate control.
 */
class MinstrelHtWifiManager : public WifiRemoteStationManager
{
  public:
    /**
     * @brief Get the type ID.
     * @return the object TypeId
     */
    static TypeId GetTypeId();
    MinstrelHtWifiManager();
    ~MinstrelHtWifiManager() override;
 
    void SetupPhy(const Ptr<WifiPhy> phy) override;
    void SetupMac(const Ptr<WifiMac> mac) override;
    int64_t AssignStreams(int64_t stream) override;
 
    /**
     * A struct to contain information of a standard.
     */
    struct StandardInfo
    {
        McsGroupType groupType{}; //!< group type associated to the given standard in Minstrel HT
        uint8_t maxMcs{};         //!< maximum MCS index (for 1 SS if 802.11n)
        MHz_u maxWidth{};         //!< maximum channel width
        std::vector<Time> guardIntervals{}; //!< supported GIs
        uint8_t maxStreams{};               //!< maximum number of spatial streams
    };
 
    /**
     * TracedCallback signature for rate change events.
     *
     * @param [in] rate The new rate.
     * @param [in] address The remote station MAC address.
     */
    typedef void (*RateChangeTracedCallback)(const uint64_t rate, const Mac48Address remoteAddress);
 
  private:
    void DoInitialize() override;
    WifiRemoteStation* DoCreateStation() const override;
    void DoReportRxOk(WifiRemoteStation* station, double rxSnr, WifiMode txMode) override;
    void DoReportRtsFailed(WifiRemoteStation* station) override;
    void DoReportDataFailed(WifiRemoteStation* station) override;
    void DoReportRtsOk(WifiRemoteStation* station,
                       double ctsSnr,
                       WifiMode ctsMode,
                       double rtsSnr) override;
    void DoReportDataOk(WifiRemoteStation* station,
                        double ackSnr,
                        WifiMode ackMode,
                        double dataSnr,
                        MHz_u dataChannelWidth,
                        uint8_t dataNss) override;
    void DoReportFinalRtsFailed(WifiRemoteStation* station) override;
    void DoReportFinalDataFailed(WifiRemoteStation* station) override;
    WifiTxVector DoGetDataTxVector(WifiRemoteStation* station, MHz_u allowedWidth) override;
    WifiTxVector DoGetRtsTxVector(WifiRemoteStation* station) override;
    void DoReportAmpduTxStatus(WifiRemoteStation* station,
                               uint16_t nSuccessfulMpdus,
                               uint16_t nFailedMpdus,
                               double rxSnr,
                               double dataSnr,
                               MHz_u dataChannelWidth,
                               uint8_t dataNss) override;
    std::list<Ptr<WifiMpdu>> DoGetMpdusToDropOnTxFailure(WifiRemoteStation* station,
                                                         Ptr<WifiPsdu> psdu) override;
 
    /**
     * Initialize all groups belonging to a given modulation class.
     *
     * @param mc the modulation class
     */
    void InitializeGroups(WifiModulationClass mc);
 
    /**
     * @param st the station that we need to communicate
     * @param packet the packet to send
     * @param normally indicates whether the normal 802.11 data retransmission mechanism
     *        would request that the data is retransmitted or not.
     * @return true if we want to resend a packet after a failed transmission attempt,
     *         false otherwise.
     *
     * Note: This method is called after any unicast packet transmission (control, management,
     *       or data) has been attempted and has failed.
     */
    bool DoNeedRetransmission(WifiRemoteStation* st, Ptr<const Packet> packet, bool normally);
 
    /**
     * Check the validity of a combination of number of streams, chWidth and mode.
     *
     * @param streams the number of streams
     * @param chWidth the channel width
     * @param mode the wifi mode
     * @returns true if the combination is valid
     */
    bool IsValidMcs(uint8_t streams, MHz_u chWidth, WifiMode mode);
 
    /**
     * Check whether a given MCS mode should be added to a given group.
     *
     * @param mode the MCS mode
     * @param groupId the group ID
     * @returns true if the MCS mode should be added to the group
     */
    bool ShouldAddMcsToGroup(WifiMode mode, std::size_t groupId);
 
    /**
     * Estimates the TxTime of a frame with a given mode and group (stream, guard interval and
     * channel width).
     *
     * @param streams the number of streams
     * @param gi guard interval duration
     * @param chWidth the channel width
     * @param mode the wifi mode
     * @param mpduType the type of the MPDU
     * @returns the transmit time
     */
    Time CalculateMpduTxDuration(uint8_t streams,
                                 Time gi,
                                 MHz_u chWidth,
                                 WifiMode mode,
                                 MpduType mpduType);
 
    /**
     * Obtain the TxTime saved in the group information.
     *
     * @param groupId the group ID
     * @param mode the wifi mode
     * @returns the transmit time
     */
    Time GetMpduTxTime(std::size_t groupId, WifiMode mode) const;
 
    /**
     * Save a TxTime to the vector of groups.
     *
     * @param groupId the group ID
     * @param mode the wifi mode
     * @param t the transmit time
     */
    void AddMpduTxTime(std::size_t groupId, WifiMode mode, Time t);
 
    /**
     * Obtain the TxTime saved in the group information.
     *
     * @param groupId the group ID
     * @param mode the wifi mode
     * @returns the transmit time
     */
    Time GetFirstMpduTxTime(std::size_t groupId, WifiMode mode) const;
 
    /**
     * Save a TxTime to the vector of groups.
     *
     * @param groupId the group ID
     * @param mode the wifi mode
     * @param t the transmit time
     */
    void AddFirstMpduTxTime(std::size_t groupId, WifiMode mode, Time t);
 
    /**
     * Update the number of retries and reset accordingly.
     * @param station the wifi remote station
     */
    void UpdateRetry(MinstrelHtWifiRemoteStation* station);
 
    /**
     * Update the number of sample count variables.
     *
     * @param station the wifi remote station
     * @param nSuccessfulMpdus the number of successfully received MPDUs
     * @param nFailedMpdus the number of failed MPDUs
     */
    void UpdatePacketCounters(MinstrelHtWifiRemoteStation* station,
                              uint16_t nSuccessfulMpdus,
                              uint16_t nFailedMpdus);
 
    /**
     * Getting the next sample from Sample Table.
     *
     * @param station the wifi remote station
     * @returns the next sample
     */
    uint16_t GetNextSample(MinstrelHtWifiRemoteStation* station);
 
    /**
     * Set the next sample from Sample Table.
     *
     * @param station the wifi remote station
     */
    void SetNextSample(MinstrelHtWifiRemoteStation* station);
 
    /**
     * Find a rate to use from Minstrel Table.
     *
     * @param station the Minstrel-HT wifi remote station
     * @returns the rate in bps
     */
    uint16_t FindRate(MinstrelHtWifiRemoteStation* station);
 
    /**
     * Update the Minstrel Table.
     *
     * @param station the Minstrel-HT wifi remote station
     */
    void UpdateStats(MinstrelHtWifiRemoteStation* station);
 
    /**
     * Initialize Minstrel Table.
     *
     * @param station the Minstrel-HT wifi remote station
     */
    void RateInit(MinstrelHtWifiRemoteStation* station);
 
    /**
     * Return the average throughput of the MCS defined by groupId and rateId.
     *
     * @param station the Minstrel-HT wifi remote station
     * @param groupId the group ID
     * @param rateId the rate ID
     * @param ewmaProb the EWMA probability
     * @returns the throughput in bps
     */
    double CalculateThroughput(MinstrelHtWifiRemoteStation* station,
                               std::size_t groupId,
                               uint8_t rateId,
                               double ewmaProb);
 
    /**
     * Set index rate as maxTpRate or maxTp2Rate if is better than current values.
     *
     * @param station the Minstrel-HT wifi remote station
     * @param index the index
     */
    void SetBestStationThRates(MinstrelHtWifiRemoteStation* station, uint16_t index);
 
    /**
     * Set index rate as maxProbRate if it is better than current value.
     *
     * @param station the Minstrel-HT wifi remote station
     * @param index the index
     */
    void SetBestProbabilityRate(MinstrelHtWifiRemoteStation* station, uint16_t index);
 
    /**
     * Calculate the number of retransmissions to set for the index rate.
     *
     * @param station the Minstrel-HT wifi remote station
     * @param index the index
     */
    void CalculateRetransmits(MinstrelHtWifiRemoteStation* station, uint16_t index);
 
    /**
     * Calculate the number of retransmissions to set for the (groupId, rateId) rate.
     *
     * @param station the Minstrel-HT wifi remote station
     * @param groupId the group ID
     * @param rateId the rate ID
     */
    void CalculateRetransmits(MinstrelHtWifiRemoteStation* station,
                              std::size_t groupId,
                              uint8_t rateId);
 
    /**
     * Estimate the time to transmit the given packet with the given number of retries.
     * This function is "roughly" the function "calc_usecs_unicast_packet" in minstrel.c
     * in the madwifi implementation.
     *
     * The basic idea is that, we try to estimate the "average" time used to transmit the
     * packet for the given number of retries while also accounting for the 802.11 congestion
     * window change. The original code in the madwifi seems to estimate the number of backoff
     * slots as the half of the current CW size.
     *
     * There are four main parts:
     *  - wait for DIFS (sense idle channel)
     *  - Ack timeouts
     *  - Data transmission
     *  - backoffs according to CW
     *
     * @param dataTransmissionTime the data transmission time
     * @param shortRetries the short retries
     * @param longRetries the long retries
     * @returns the unicast packet time
     */
    Time CalculateTimeUnicastPacket(Time dataTransmissionTime,
                                    uint32_t shortRetries,
                                    uint32_t longRetries);
 
    /**
     * Perform EWMSD (Exponentially Weighted Moving Standard Deviation) calculation.
     *
     * @param oldEwmsd the old EWMSD
     * @param currentProb the current probability
     * @param ewmaProb the EWMA probability
     * @param weight the weight
     * @returns the EWMSD
     */
    double CalculateEwmsd(double oldEwmsd, double currentProb, double ewmaProb, double weight);
 
    /**
     * Initialize Sample Table.
     *
     * @param station the Minstrel-HT wifi remote station
     */
    void InitSampleTable(MinstrelHtWifiRemoteStation* station);
 
    /**
     * Printing Sample Table.
     *
     * @param station the Minstrel-HT wifi remote station
     */
    void PrintSampleTable(MinstrelHtWifiRemoteStation* station);
 
    /**
     * Printing Minstrel Table.
     *
     * @param station the Minstrel-HT wifi remote station
     */
    void PrintTable(MinstrelHtWifiRemoteStation* station);
 
    /**
     * Print group statistics.
     *
     * @param station the Minstrel-HT wifi remote station
     * @param groupId the group ID
     * @param of the output file stream
     */
    void StatsDump(MinstrelHtWifiRemoteStation* station, std::size_t groupId, std::ofstream& of);
 
    /**
     * Check for initializations.
     *
     * @param station the Minstrel-HT wifi remote station
     */
    void CheckInit(MinstrelHtWifiRemoteStation* station);
 
    /**
     * Count retries.
     *
     * @param station the Minstrel-HT wifi remote station
     * @returns the count of retries
     */
    uint32_t CountRetries(MinstrelHtWifiRemoteStation* station);
 
    /**
     * Update rate.
     *
     * @param station the Minstrel-HT wifi remote station
     */
    void UpdateRate(MinstrelHtWifiRemoteStation* station);
 
    /**
     * Return the rateId inside a group, from the global index.
     *
     * @param index the index
     * @returns the rate ID
     */
    uint8_t GetRateId(uint16_t index);
 
    /**
     * Return the groupId from the global index.
     *
     * @param index the index
     * @returns the group ID
     */
    std::size_t GetGroupId(uint16_t index);
 
    /**
     * Returns the global index corresponding to the groupId and rateId.
     *
     * For managing rates from different groups, a global index for
     * all rates in all groups is used.
     * The group order is fixed by BW -> SGI -> streams.
     *
     * @param groupId the group ID
     * @param rateId the rate ID
     * @returns the index
     */
    uint16_t GetIndex(std::size_t groupId, uint8_t rateId);
 
    /**
     * Returns the Id of a MCS of a given modulation class with the given number of streams, GI and
     * channel width used in the group associated to that modulation class.
     *
     * @param mc the modulation class
     * @param streams the number of streams
     * @param guardInterval guard interval duration
     * @param chWidth the channel width
     * @returns the HT group ID
     */
    std::size_t GetIdInGroup(WifiModulationClass mc,
                             uint8_t streams,
                             Time guardInterval,
                             MHz_u chWidth);
 
    /**
     * Returns the number of groups for a given modulation class.
     *
     * @param mc the modulation class
     * @returns the number of groups for the modulation class
     */
    std::size_t GetNumGroups(WifiModulationClass mc);
 
    /**
     * Returns the groupId of an HT MCS with the given number of streams, GI and channel width used.
     *
     * @param streams the number of streams
     * @param guardInterval guard interval duration
     * @param chWidth the channel width
     * @returns the HT group ID
     */
    std::size_t GetHtGroupId(uint8_t streams, Time guardInterval, MHz_u chWidth);
 
    /**
     * Returns the groupId of a VHT MCS with the given number of streams, GI and channel width used.
     *
     * @param streams the number of streams
     * @param guardInterval guard interval duration
     * @param chWidth the channel width
     * @returns the VHT group ID
     */
    std::size_t GetVhtGroupId(uint8_t streams, Time guardInterval, MHz_u chWidth);
 
    /**
     * Returns the groupId of an HE MCS with the given number of streams, GI and channel width used.
     *
     * @param streams the number of streams
     * @param guardInterval guard interval duration
     * @param chWidth the channel width
     * @returns the HE group ID
     */
    std::size_t GetHeGroupId(uint8_t streams, Time guardInterval, MHz_u chWidth);
 
    /**
     * Returns the groupId of an EHT MCS with the given number of streams, GI and channel width
     * used.
     *
     * @param streams the number of streams
     * @param guardInterval guard interval duration
     * @param chWidth the channel width
     * @returns the EHT group ID
     */
    std::size_t GetEhtGroupId(uint8_t streams, Time guardInterval, MHz_u chWidth);
 
    /**
     * Returns the group ID of an MCS of a given group type with the given number of streams, GI and
     * channel width used.
     *
     * @param type the MCS group type
     * @param streams the number of streams
     * @param guardInterval guard interval duration
     * @param chWidth the channel width
     * @returns the group ID
     */
    std::size_t GetGroupIdForType(McsGroupType type,
                                  uint8_t streams,
                                  Time guardInterval,
                                  MHz_u chWidth);
 
    /**
     * Returns the lowest global index of the rates supported by the station.
     *
     * @param station the Minstrel-HT wifi remote station
     * @returns the lowest global index
     */
    uint16_t GetLowestIndex(MinstrelHtWifiRemoteStation* station);
 
    /**
     * Returns the lowest global index of the rates supported by in the group.
     *
     * @param station the Minstrel-HT wifi remote station
     * @param groupId the group ID
     * @returns the lowest global index
     */
    uint16_t GetLowestIndex(MinstrelHtWifiRemoteStation* station, std::size_t groupId);
 
    /**
     * Returns a list of only the MCS supported by the device for a given modulation class.
     * @param mc the modulation class
     * @returns the list of the MCS supported for that modulation class
     */
    WifiModeList GetDeviceMcsList(WifiModulationClass mc) const;
 
    /**
     * Given the index of the current TX rate, check whether the channel width is
     * not greater than the given allowed width. If so, the index of the current TX
     * rate is returned. Otherwise, try halving the channel width and check if the
     * MCS group with the same number of streams and same GI is supported. If a
     * supported MCS group is found, return the index of the TX rate within such a
     * group with the same MCS as the given TX rate. If no supported MCS group is
     * found, the simulation aborts.
     *
     * @param txRate the index of the current TX rate
     * @param allowedWidth the allowed width
     * @return the index of a TX rate whose channel width is not greater than the
     *         allowed width, if found (otherwise, the simulation aborts)
     */
    uint16_t UpdateRateAfterAllowedWidth(uint16_t txRate, MHz_u allowedWidth);
 
    Time m_updateStats;            //!< How frequent do we calculate the stats.
    Time m_legacyUpdateStats;      //!< How frequent do we calculate the stats for legacy
                                   //!< MinstrelWifiManager.
    uint8_t m_lookAroundRate;      //!< The % to try other rates than our current rate.
    uint8_t m_ewmaLevel;           //!< Exponential weighted moving average level (or coefficient).
    uint8_t m_nSampleCol;          //!< Number of sample columns.
    uint32_t m_frameLength;        //!< Frame length used to calculate modes TxTime in bytes.
    std::size_t m_numGroups;       //!< Number of groups Minstrel should consider.
    uint8_t m_numRates;            //!< Number of rates per group Minstrel should consider.
    bool m_useLatestAmendmentOnly; //!< Flag if only the latest supported amendment by both peers
                                   //!< should be used.
    bool m_printStats;             //!< If statistics table should be printed.
 
    MinstrelMcsGroups m_minstrelGroups; //!< Global array for groups information.
 
    Ptr<MinstrelWifiManager> m_legacyManager; //!< Pointer to an instance of MinstrelWifiManager.
                                              //!< Used when 802.11n/ac/ax not supported.
 
    Ptr<UniformRandomVariable> m_uniformRandomVariable; //!< Provides uniform random variables.
 
    TracedValue<uint64_t> m_currentRate; //!< Trace rate changes
};
 
} // namespace ns3
 
#endif /* MINSTREL_HT_WIFI_MANAGER_H */